The objective of this proposal is to delineate the precise role that IgG antibodies, surface antigens and antigen-antibody complexes derived from surface antigens and their respective antibodies play in regulating cytotoxic T-cell development. The primary focus of this investigation will be on demonstrating that a primary cytotoxic T-cell response is regulated by an antigen-driven suppressor cell whereas a secondary response is modulated by an antigen-antibody complex-triggered suppressor cell. To induce suppressor cells in primary immune response, heat-inactivated tumor cells will be used. Secondary cytotoxic T-cell response can be induced by heat-inactivated cells and inhibited by antibodies. The observed inhibition by antibody-coated cells appears to be mediated by antigen-antibody complexes. We are studying the effects of antigen vs antigen-antibody induced suppression in a well-defined in vitro induction system, using 51Cr-release assay for cytotoxic activity of T cells. These studies will allow characterization of the suppressor cells involved with respect to drug sensitivities, surface markers and adherence properties.